The evolution of wireless communication over the past century, since Guglielmo Marconi's 1897 demonstration of radio's ability to provide continuous contact with ships sailing the English Channel, has been remarkable. Since Marconi's discovery, new wireline and wireless communication methods, services and standards have been adopted by people throughout the world. This evolution has been accelerating, particularly over the last ten years, during which the mobile radio communications industry has grown by orders of magnitude, fueled by numerous technological advances that have made portable radio equipment smaller, cheaper and more reliable. The exponential growth of mobile telephony will continue to rise in the coming decades as well, as this wireless network interacts with and eventually overtakes the existing wireline networks.
With reference now to FIG. 1 of the drawings, there is illustrated a Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a mobile station (MS) 20 may move freely without having to send update location information to the MSC/VLR area 12 that controls that LA 18. Each Location Area 12 is divided into a number of cells 22. Mobile Station (MS) 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other and other wireline and wireless users outside the network 10. A Base Station (BS) 24 is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical area of the cell 22 in which to handle radio traffic to and from the MS 20.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location and routing information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 26 may be co-located with a given MSC 14, an integral part of the MSC 14 or service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the mobile stations 20 currently located within the MSC/VLR area 12. If a mobile station 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 will request data about that mobile station 20 from the HLR database 26 (simultaneously informing the HLR 26 about the current location of the mobile station 20). Accordingly, if the user of the mobile station 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26.
In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectfully, contain various subscriber information associated with a given mobile station 20. It should be understood that while the MS 20 user remains within the confines of the subscribed network, i.e., the cellular network 10, all services may be handled by the subscribed network. As the MS 20 travels or roams into different networks, i.e., different PLMNs 10, the neighboring network operators can provide similar services to the MS 20 user. Frequently, Service Providers (SP) of the PLMNs 10 cooperate with each other in an effort to offer their respective subscribers a coverage area much wider than any one of them could do on their own. As is understood in this area, administrative issues like charging, subscription agreements and other details must be solved between the different operators or SPs, in addition to the technical details to make the roaming possible, e.g., transfers of location data between networks, the existence of a common access interface, etc.
Unfortunately, not all such Service Providers are acceptable to a roaming MS 20. Indeed, under current requirements for Personal Communications Services (PCS) phones, an SP may be designated in various ways: as a home_provider_owned (home) service; a partner SP, with which the home provider has negotiated for superior subscriber services and rates; a favored SP, which is similar to the aforedescribed partner SP status, except the service area of the favored SP overlaps the service area of the home SP; a forbidden SP is a Service Provider that a roaming subscriber should never use, with the obvious exception of 911 services; and a neutral SP is one that is none of the other designations listed. Home and partner SP services have a higher priority than favored or neutral services.
In view of the above nomenclature, an Acceptable SP may be defined as a home or partner SP and an Unacceptable SP is favored or neutral. A forbidden SP does not enter this equation and is not considered, except as discussed in emergency situations. The actual mechanism for determining the acceptability of a detected SP involves comparing the SP's System Identification (SID) number and System Operator Code (SOC) against a home record of the home SID and SOC and against the respective lists of SIDs and SOCs for partner, favored and forbidden SPs, all of which may be stored in memory within the MS 20. Any SP that has no match is considered neutral.
While an MS 20 is roaming, particularly if following Intelligent Roaming (IR) protocols, the MS 20 must perform periodic triggered rescans of the available providers if not then camped on an Acceptable SP. As is understood in the art, a change in control channel triggers a scan and a control channel flag (CCH_FLAG) is utilized to monitor such changes. The periodicity of the scan is preferably stored within an IR database 21 stored within a memory module 20A within the MS 20, as shown in FIG. 2.
A problem arises when the MS 20 inadvertently camps on a Non-Acceptable SP while an Acceptable SP is present but was temporarily not accessible. This could happen for a variety of reasons. For example, the Acceptable SP is temporarily not seen by the MS 20 due to transient radio frequency (RF) conditions such as signal blockage or shading due to buildings or natural obstructions. Another instance is where the MS 20 is in an area where no system, Acceptable or not, are seen, e.g., a metal elevator car. Although all systems become simultaneously available, i.e., upon opening the elevator door, the MS 20 during its scan protocol may have already marked the particular band for the Acceptable SP as empty (before the door opened) just prior to scanning the band of the Unacceptable SP.
Since a conventional rescan timer 28, also within said MS 20, as illustrated in FIG. 2, generally waits approximately 15-20 minutes before reinitiating another scan, with the minimum wait being approximately 6 minutes, 24 seconds (300 hyperframes), this is too long a time for the user to wait in order to find the now-accessible Acceptable SP. Since most experienced users know that they should have acceptable service in a given area, they may accept the inconvenience of a temporary, i.e., on the order of seconds, loss of service with the Acceptable SP. Six or more minutes of inconvenience, however, is a far different matter, and the user will perceive that the MS 20 is permanently on the wrong SP. It has been discovered that an obvious solution, shortening the duration of the timer 28, is generally not feasible because this results in degraded page performance, i.e., the MS 20 cannot receive pages while it is doing a triggered scan.
Also, it is desired to avoid excessive scanning of available frequencies if the MS 20 is stationary since if an Acceptable SP has not been found, there is no need to retry until going to a new location.
It is, accordingly, an object of the present invention to provide a system and method for improved rescanning by an MS 20 for an available and Acceptable Service Provider.
It is also an object of the present invention to provide an improved apparatus and method for shortening the time a mobile terminal takes to rescan for an Acceptable Service Provider.
It is a further object of the present invention to provide an improved apparatus and method for performing successive scans by the mobile terminal after failure to find an Acceptable SP.
It is a still further object of the present invention to prevent excessive rescanning by the mobile terminal.